Individuals typically require a comfortable surface, or mattress, on which to recline while sleeping or resting. A variety of applications, such as construction, require a cushioning and/or elevation mechanism. For sleeping or resting, mattresses may be used in both a semi-permanent and a temporary manner. In temporary applications the mattress is removed and stored or rearranged for alternate use when sleeping or resting is ended. A typical alternate use for such a mattress is as a cushion for a sofa or futon. Further, lightweight portable mattresses find use in many other areas. In particular, individuals involved in activities such as camping and backpacking need a mattress which is portable, lightweight, puncture resistant, inflatable or self-inflatable, insulating, and comfortable.
Mattresses intended for camping and backpacking have used a number of approaches to obtain these properties. They include: a) basic chambered air mattresses; b) simple thin resilient insulating pads; c) open-cell resilient foam pads (typically 1 to 2 inches thick); and d) a variety of insulated air mattresses.
Basic chambered air mattresses have been found deficient in several aspects. These mattresses provide very little insulating benefit. Typically such mattresses use a coated synthetic or natural fabric or a plastic sheeting material to form the air-impervious envelope. Where provided, similar materials are used to limit the displacement between the top and bottom envelope surfaces. The substantially non-stretchable nature of these materials limit the capacity of the envelope to respond to sudden pressure surges which can lead to bond failure. Under cold weather conditions, a user loses an excessive amount of heat through the air mattress. An excessive amount of time and effort may be required to inflate these mattresses. Further, all comfort benefits are lost when the mattress is deflated by an accidental puncture. Finally, they provide only moderate comfort benefits.
Thin pads fabricated from natural and synthetic materials also have been used as mattresses. Pads made of natural materials tend to be relatively heavy and provide very little cushioning benefit. Pads made from synthetic materials, such as closed-cell vinyl-nitrile (Ensolite), ethylene-vinyl acetate (EVA), or polyethylene foam, addressed the weight problem but provide only a limited comfort benefit. Under moderate conditions, typically spring, summer, fall, and temperate winters, 3/8th inch thick synthetic pads commonly have been used as mattresses. One-half inch and thicker pads have been used for extreme conditions. Pads made from thermoformed closed-cell foams are described in U.S. Pat. No. 4,980,936 to Frickland et al. That patent also presents extensive background material on the use of foamed pads. Although closed-cell foam pads could be made thicker, this would increase weight and reduce portability.
The compressibility of open-cell foam sheets, such as polyurethane, has enabled the use of thicker materials, typically ranging from 1.0 to 2.5 inches thick. This increased thickness makes the mattress somewhat more comfortable at the expense of increased weight. For the foam to have sufficient resistance to compression to provide an adequate degree of comfort, foams having a 25% ILD (indention load deflection) of at least about 35 pounds have been used. The comfort benefit of such mattresses is limited due to the characteristics of the human form. When reclining on one's back, pressure points are created at the shoulder, hips, and heels. This focuses most of the weight of the individual on only a small portion of the overall mattress surface. To increase resilience sufficiently to support these pressure points adequately may require increasing, in some combination, the density or thickness of the foam sheet and thus the weight. Furthermore, if higher resilience foams and/or thicker foams are used to give more support, the foam sheet is more difficult to roll up compactly when not in use. These open-cell mattresses also absorb water, which is an obvious problem for products intended for outdoor use. Covering the mattress with a water resistant material increases weight and is not always effective at keeping the foam dry.
Thereafter, inventors created several versions of insulated air mattresses. These designs completely or partially filled an air mattress shell with resilient insulating materials. One such is shown in Swiss Pat. No. 428,124, where the mattress comprises an outer rectangular shaped air-impervious envelope and a foam interior core. The patent notes that the air mattress can be compressed into a stowed position (i.e., rolled up to a relatively small volume) after which the inflating valve of the air mattress is closed to maintain the mattress in its compact stowed configuration. When the valve is opened, the force of the resilient foam core causes the mattress to self-inflate to its expanded position, after which the valve is closed to contain the entrapped air.
A related concept is disclosed in U.S. Pat. No. 4,694,515, which describes a self-inflating air mattress coupled to a foldable bed frame. The airtight mattress envelope encloses resilient means urging the upper and lower faces apart. This approach relies upon the bed frame for the dimensional rigidity necessary to maintain the mattress in a fully extended horizontal position during inflation. When utilizing a lightweight flexible cover material without this separate frame component, the flexible cover edges of the mattress tend to draw together causing the top cover to sag during the self-inflation process and the mattress would only partially inflate when the valve was opened. Further, insulating means, separate from the cover material and resilient means, must be provided.
A somewhat related concept is disclosed in U.S. Pat. No. 2,997,100, which describes a foam filled mattress of a design more commonly used for a conventional household bed. The envelope of this mattress is airtight and can be inflated to a desired pressure, with the air pressure providing a certain degree of additional support for a heavier person.
Another approach to providing a self-inflating foam filled air mattress is disclosed in U.S. Pat. No. 3,798,686. In this patent the resistance of the foam core to compression is utilized in the same manner as the mattress of the abovementioned Swiss patent to give the air mattress its self-inflating characteristic. The foam core shown in this patent comprises upper and lower continuous sheets of open-celled foam, between which are two layers of crossing foam ribs arranged in a lattice. The foam components are all bonded to one another, and the entire structure is enclosed within a flexible envelope, preferably of a air-impervious nylon type. As such this design does not utilize the compression resistance of the foam to any great degree. Rather, it utilizes the foam to enable self-inflation. This design relies upon the upper and lower continuous sheets of open-cell foam for much of its insulating benefit. This, together with the separate air-impervious cover, leads to the weight penalty associated with the previously mentioned simple open-cell foam sheet mattress.
U.S Pat, No. 4,688,283 to Jacobson, et al. discloses a multi-chambered mattress which utilizes an open-cell foam within a air-impervious nylon cover. Multiple chambers with differing thicknesses of foam are provided. Selected chamber pairs are interconnected to enable the free passage of air between these chambers. The cover is sealed and air valves are provided to enable the independent inflation and deflation of each chamber or interconnected chamber group. The level of support may be varied somewhat by increasing or decreasing the volume of air enclosed within the chambers. This design also relies upon a significant quantity of open-cell foam materials. This foam together with the air-impervious cover leads to the weight penalty.
U.S Pat. Nos. 4,025,974 and 4,624,877 to Lea, et al. disclose a single chamber design which encloses a slab of open-cell foam. The patentees laminate the top and bottom surfaces of an open-cell foam to the inside of a cover made of an air-impervious plastic-coated fabric. Typically a nylon fabric coated with polyurethane ('974) or laminated to solid polymer films is used as the cover. Under the application of heat, the fabric coating softens and bonds with the surface of the open-cell foam slab. This bonding reduces displacement ("ballooning" or "billowing") of the covers and enables better pressure management. Billowing occurs when top and bottom covers are inadequately linked mechanically to each other and are free to expand from one another. Unless it is limited properly, this billowing creates an unstable surface and provides inconsistent support for the user. The foam acts as a compression member in areas of a direct load and as a tension member in areas removed from a direct load. Tensioning of the foam remote from the area of compression causes the pressure to rise in the pad, further resisting the local compression. As such, support is increased at the pressure points. As with the other self-inflating insulated air-mattresses described above, the use of solid open-cell foam sheet and separate air-impervious cover components significantly increases mattress weight. Perforation of the open-cell foam sheet to reduce weight would; a) reduce insulation; b) lead to destructive delamination between the foam sheet and the cover element; c) diminish the mattress's horizontal dimensional rigidity. The insulation value of the open-cell foam sheet is critical since the cover does not provide significant insulating value. In U.S. Pat. No. 4,025,974 at Column 10, lines 14-19 and at Column 11, lines 40-47 it is stressed that it is necessary to bond the cover to the foam-sheet along substantially the entire horizontal surface because there is a tendency when a small area of non-bonding or delamination occurs in an area where the skin is tensioned outwardly for this delamination to spread progressively, even under moderate pressure. As the unbonded area spreads outwardly, the delaminating force at the edge of the delaminating area increases. Given the inflated profile of the cover and open-cell foam sheet when bonded together, perforation of the open-cell foam sheet of U.S. Pat. No. 4,025,974 would accelerate the delamination process. Because of the flexible nature of the air-impervious cover, this design relies upon the open-cell foam sheet for the dimensional rigidity necessary for proper inflation. Extensive perforation of the open-cell foam sheet, to reduce weight, would severely limit the air drawn into the mattress during the self-inflation process. Because of the flexibility of the covers, their edges would tend to draw together and the covers would sag over the void areas during the self-inflation process.
As additional background information, other examples of foam filled structures are disclosed in the following patents: British Pat. No. 984,604; Brawner U.S. Pat. No. 1,159,166; Nappe U.S. Pat. No. 2,834,970; Lerman U.S. Pat. No. 3,323,151; Cornes U.S. Pat. No. 3,378,864; Kain U.S. Pat. No. 3,537,116; and Gottfried U.S. Pat. No. 3,611,455. In U.S. Pat. No. 4,092,750 a metallized film is used in the mattress's interior for added insulation.
Even with the use of tough coated synthetic fabrics, these mattresses are susceptible to punctures. A foreign object only has to penetrate between fabric stands and puncture the very thin polymer coating. Previous designs have focused upon the use of very thin materials, typically in the range of about 4 mils to about 15 mils. When such a mattress is punctured, air pressure is lost, and the mattress's support is reduced.
Finally, the mattress's comfort is limited by the fully sealed nature of the mattress. This limits the mattress's ability to respond to changing conditions, such as switching from lying on one's back to lying on one's side. One example of an attempt to eliminate this limitation is presented in U.S. Pat. No. 4,328,083 to Lineback. This approach locates one or more resilient sub-chambers within the confines of the larger air mattress envelope. When force is applied to the air mattress, the enclosed fluid presses against the resilient sub-chambers. Being open to the atmosphere, these chambers deform, releasing air to the atmosphere, thereby partially releasing pressure within the primary chamber. The fixed resilience of these sub-chambers restrict the ability of the air mattress to respond to individuals with differing weights and to individual preferences.
While the prior art has recognized the value of using an air-impervious inflatable envelope, a variety of mechanical linkages between bottom and top mattress surfaces, frames, separate self-inflation means, insulating, and comfort enhancement components in various combinations, the prior art failed to recognize that by choosing materials having appropriate properties as components of a mattress those properties may be utilized in combination to reduce the amount of or even eliminate components. This allows reduction of weight while optimizing such qualities as portability, puncture resistance, inflatability, insulation and comfort.